Extendable electrode for gas discharge laser

ABSTRACT

A movable electrode assembly for use in a laser system, includes a first electrode having a first discharge surface, a second electrode having a second discharge surface. The second electrode being arranged opposite from the first electrode. The second discharge surface being spaced apart from the first discharge surface by a discharge gap. A discharge gap adjuster interfaced with at least one of the second electrode or the first electrode, the discharge gap adjuster configured to adjust the discharge gap. A method of adjusting a discharge gap is also disclosed.

PRIORITY CLAIM

This application is a divisional of and claims priority from U.S. patentapplication Ser. No. 12/945,719 filed on Nov. 12, 2010 and entitled“Extendable Electrode For Gas Discharge Laser,” which is incorporatedherein by reference in its entirety for all purposes. The Ser. No.12/945,719 application is a continuation of and claims priority fromU.S. patent application Ser. No. 11/787,463 filed on Apr. 16, 2007 nowU.S. Pat. No. 7,856,044 and entitled “Extendable Electrode For GasDischarge Laser,” which is incorporated herein by reference in itsentirety for all purposes. The Ser. No. 11/787,463 application is acontinuation-in-part application of co-owned U.S. patent applicationSer. No. 10/854,614, filed on May 25, 2004 and issued as U.S. Pat. No.7,218,661, Entitled “Line Selected F.sub.2 Two Chamber Laser System”which issued on May 15, 2007 and which is a continuation of U.S. patentapplication Ser. No. 10/056,619, filed on Jan. 23, 2003 and issued asU.S. Pat. No. 6,801,560, Entitled “Line Selected F.sub.2 Two ChamberLaser System”, which issued on Oct. 5, 2004, which is acontinuation-in-part of U.S. patent application Ser. No. 09/768,753,filed on Jan. 23, 2001 and issued as U.S. Pat. No. 6,414,979, Entitled“Gas Discharge Laser with Blade-Dielectric Electrode”, which issued onJul. 2, 2002, the entire contents of each of which are herebyincorporated by reference herein for all purposes.

RELATED APPLICATIONS AND PATENTS

The present application is related to U.S. Pat. No. 6,466,602, Entitled“Gas Discharge Laser Long Life Electrodes”, which issued on Oct. 15,2002, the entire contents of each of which are hereby incorporated byreference herein for all purposes.

BACKGROUND

The present application relates generally to gas discharge lasersystems. The present application is particularly, but not exclusivelyuseful as an extendable electrode system for a transverse discharge gaslaser.

Electrode erosion in high-pressure transverse discharge lasers isusually the mechanism that limits their operational lifetime. Theerosion of one or both of the electrodes is typically caused by thecombined attack of fast ions and electrons from the current discharge.As the electrodes wear, the inter-electrode spacing increases to thepoint where the operational characteristics of the laser are so severelyaffected that laser operation must be stopped. The gain generator mustthen be refurbished with new electrodes in order to re-establish thecorrect electrode spacing.

In an attempt to increase laser lifetime, Japanese Patent ApplicationJP06-029592 filed on Jun. 10, 1991 and titled “Discharge-Pumped Laser”discloses a scheme “to regulate an interval between electrodes inaccordance with consumption of a discharge part of the electrode and toalways hold a discharging width constant by providing moving means forat least one of discharge electrode pair toward the other electrode.”However, to applicant's knowledge, such a relatively simplistic systemhas yet to be successfully commercialized.

Since 1991 when Japanese Patent Application JP06-029592 was filed, gasdischarge lasers have evolved substantially. Modern transverse dischargelasers are now designed to produce a relatively high power output(having both a relatively high pulse energy and high pulse repetitionrate) with relatively tight specifications on beam properties such asbandwidth and pulse-to-pulse energy stability, to name just a few. Toachieve this performance, modem transverse discharge lasers typicallyinclude complex, highly engineered discharge chambers. For example, arelatively low impedance, low inductance current path geometry istypically provided in the chamber to conduct the extremely high peakcurrents that are generated by an electrical drive circuit to theelectrodes. Also, the chamber may need to provide suitable heat transferpaths, for example, to prevent component overheating, and in particular,electrode overheating. In addition to heat transfer paths, the chambermay need to provide suitable gas flow paths to reduce gas flowturbulence and ensure that a fresh quantity of laser gas is positionedbetween the electrodes prior to the initiation of the next discharge.Concurrent with the above-described engineering constraints, the chambermay need to provide suitable component geometries which prevent orminimize the impact of reflected acoustic waves which can reach thedischarge area and adversely affect properties of the output laser beamsuch as bandwidth, divergence, etc.

With the above considerations in mind, Applicants disclose an extendableelectrode system for a gas discharge laser.

SUMMARY

Disclosed herein are systems and methods for extending one or both ofthe discharge electrodes in a transverse discharge laser chamber inwhich the electrodes are subject to a dimensional change due to erosion.Electrode extension can be performed to increase the chamber life,increase laser performance over the life of the chamber, or both.Operationally, the inter-electrode spacing may be adjusted to maintain aspecific target gap distance between the electrodes or to optimize aspecific parameter of the laser output beam such as bandwidth,pulse-to-pulse energy stability, beam size, etc.

As disclosed herein, control of the inter-electrode spacing may beeffectuated in several different ways. In one implementation, theinter-electrode spacing may be visually observed and the observationused to move one or both of the electrodes. For example, a technicianmay manually instruct a laser system controller via keypad or graphicuser interface to signal an actuator, which in turn, produces thedesired inter-electrode spacing adjustment.

In another implementation, the inter-electrode spacing may be adjustedusing a feedback loop. For example, a controller may be provided tomonitor a device parameter and generate a control signal indicative ofthe parameter. For use with the controller, an actuator may be operablycoupled with one or both of the electrodes, the actuator responsive tothe control signal to move one or both of the electrodes and adjust theinter-electrode spacing. For this implementation, the parameter may beprovided to the controller by an on-board measuring instrument or otherlaser component as described below. The parameter can include, but isnot necessarily limited to wavelength, bandwidth, pulse-to-pulse energystability, beam size, accumulated pulse count, average historical dutycycle, a measured relationship between discharge voltage and pulseenergy or combinations thereof.

In a particular implementation, a controller may be programmed to scanthe inter-electrode spacing over a pre-determined spacing range. Duringthe scan, a measuring instrument or other laser component may provideone or more parameter inputs to the controller allowing the controllerto determine a relationship between the parameter and theinter-electrode spacing. From the relationship, the controller maydeduce an optimum inter-electrode spacing and thereafter adjust theinter-electrode spacing accordingly.

Several mechanisms capable of being coupled to an electrode to producean actuator-driven, electrode movement are disclosed herein. In onemechanism, a first elongated rigid member having sawtooth ramp structureand a second elongated rigid member having complimentary sawtooth rampstructure are provided. The ramp structures are aligned longitudinallyand placed in contact with each other. The first rigid member may beattached to an electrode and the second rigid member attached to anactuator such that movement of the actuator translates the second rigidmember in the direction of member elongation. With this structuralarrangement, longitudinal movement of the second rigid member causes amovement of the first rigid member (and the attached electrode) in adirection normal to the direction of member elongation. Other electrodemovement mechanisms are disclosed in further detail below including acam-operated mechanism and a screw-operated mechanism.

For use in conjunction with one or more of the electrode movementmechanisms described above, a conductive, flexible member may beprovided for electrically shielding moving parts and/or contact surfacesof the mechanism from the fields generated during an electrodedischarge. For example, the flexible member may extend from a firstflexible member edge that is attached to one of the electrodes formovement therewith to a second flexible member edge that is held fixedrelative to the housing. In some cases, the flexible member may beformed with one or more convolutions that are aligned parallel to thedirection of electrode elongation to impart flexibility to the member.In one embodiment, the second edge of the flexible member may beelectrically connected to a plurality of so-called “current tines” whichprovide a low impedance path from the moveable electrode to a pulsepower supply.

In another implementation, a movable electrode assembly for use in lasersystem includes a first electrode, a second electrode arranged oppositefrom the first electrode, the second electrode being spaced apart fromthe first electrode by a discharge gap and a discharge gap adjusterinterfaced with at least one of the second electrode or the firstelectrode, the discharge gap adjuster configured to adjust the dischargegap. The discharge gap adjuster can include at least one screw incontact with at least one of the second electrode or the firstelectrode. The discharge gap adjuster can include at least cam incontact with at least one of the second electrode or the firstelectrode.

In another implementation, a movable electrode assembly for integrationinto a housing of a laser system includes a first electrode having adischarge surface, a second electrode having a discharge surface, suchthat the discharge surface of the first electrode and the dischargesurface of the second electrode face each other in a spaced apartsetting that defines a desired discharge gap, and a mechanism formoveably adjusting the spaced apart setting toward the desired dischargegap.

In another implementation, a method of adjusting a discharge gapincludes moving a first elongated member longitudinally relative to asecond elongated member, the first elongated member having a firstinclined face, the first inclined face being inclined longitudinallyalong the first elongated member, the second elongated member having asecond inclined face, the second inclined face being inclinedlongitudinally along the second elongated member, the second inclinedface being substantially complimentary to the first inclined face,wherein a second electrode is coupled to the first elongated member anda first electrode is opposite from the second electrode, the secondelectrode being separated from the first electrode by a discharge gap.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings.

FIG. 1 shows a simplified, perspective, partially exploded view of atransverse discharge gas laser.

FIG. 2 shows a simplified schematic view of a multi-stage laser system.

FIGS. 3A-D each schematically show a pair of electrodes viewed as seenalong line 3A-3A in FIG. 1 with FIG. 3A showing the electrodes in theirinitial positions prior to erosion, FIG. 3B showing the electrodes aftererosion, FIG. 3C showing the electrodes after erosion and after one ofthe electrodes has been moved to adjust the inter-electrode spacing andFIG. 3D showing the case where one electrode is moved into the initialelectrode gap to accommodate erosion of the other electrode.

FIGS. 4A-G show the components of a mechanism that may be coupled to anelectrode to produce an actuator-driven, electrode movement, where FIGS.4A and 4B schematically show a pair of electrodes viewed as seen alongline 3A-3A in FIG. 1 with FIG. 4A showing the electrode in a retractedstate relative to the electrode support bar and FIG. 4B showing theelectrode in an extended state relative to the electrode support bar;FIGS. 4C and 4D show perspective, simplified views of a rigid sawtoothstructure and a complementary rigid sawtooth structure, respectively;FIGS. 4E and 4F show a moveable electrode viewed as seen along line4E-4E in FIG. 1 with FIG. 4E showing the electrode in a retracted staterelative to the electrode support bar and FIG. 4F showing the electrodein an extended state relative to the electrode support bar; and FIG. 4Gshows a linkage including a push rod and pivoting lever for establishinga mechanical path between an actuator and a rigid sawtooth structure.

FIG. 5 shows a perspective view of a moveable electrode assemblyillustrating a flexible conductive member electrically connecting themoveable electrode to a plurality of current return tines.

FIGS. 6A and 6B show the components of another mechanism having acamshaft that may be coupled to an electrode to produce anactuator-driven, electrode movement, where FIGS. 6A and 6B schematicallyshow a pair of electrodes viewed as seen along line 3A-3A in FIG. 1 withFIG. 6A showing the electrode in a retracted state relative to theelectrode support bar and FIG. 6B showing the electrode in an extendedstate relative to the electrode support bar.

FIGS. 7A-E show the components of drive screw mechanisms that may becoupled to an electrode to produce an actuator-driven, electrodemovement, where FIGS. 7A and 7B schematically show a pair of electrodesviewed as seen along line 3A-3A in FIG. 1 with FIG. 7A showing theelectrode in a retracted state relative to the electrode support bar andFIG. 7B showing the electrode in an extended state relative to theelectrode support bar; FIGS. 7C-7E show a moveable electrode viewed asseen along line 4E-4E in FIG. 1 with FIG. 7C showing a mechanism havinga single drive screw, FIG. 7D showing a mechanism having two drivescrews, and FIG. 7E showing a mechanism having a three drive screws.

FIGS. 8A and 8B show the components of a device having moveable flowguides to accommodate extension of electrodes having non-parallelsidewalls, where FIGS. 8A and 8B schematically show a pair of electrodesviewed as seen along line 3A-3A in FIG. 1 with FIG. 8A showing theelectrode in a retracted state relative to the electrode support bar andFIG. 8B showing the electrode in an extended state relative to theelectrode support bar.

FIG. 9 shows a moveable electrode viewed as seen along line 4E-4E inFIG. 1 having an electrode end contour to accommodate electrodeextension.

DETAILED DESCRIPTION

Referring initially to FIG. 1, a simplified, partially exploded view ofportions of a transverse discharge gas laser device are shown andgenerally designated 20. For example, the device 20 may be a KrF excimerlaser, an XeF excimer laser, an XeCl excimer laser, an ArF excimerlaser, a molecular fluorine laser or any other type of transversedischarge gas laser known in the pertinent. As shown, the device 20 mayinclude a two-part chamber housing 22 a, b being formed of a chamberwall that may be made of a conductive, corrosion resistant material,e.g., nickel-plated aluminum. As further shown in FIG. 1, windowassemblies 24 a, b may be provided at each end of the chamber housing 22a, b to allow light to enter, exit and pass through the chamber housing22 a,b along a common beam path. With this structure, the hollow chamberhousing 22 a, b and window assemblies 24 a, b may surround a volumewhich holds a laserable gas medium under pressure together with othercomponents suitable to create a discharge in the medium. These othercomponents may include, for example, a pair of discharge electrodes (notshown in FIG. 1), a fan to circulate the gas (not shown in FIG. 1), heatexchangers to cool the gas (not shown in FIG. 1), etc. It is to beappreciated that the chamber housing 22 a,b may also be formed with anumber of sealed inlets/outlets (not shown in FIG. 1), to allow gas tobe introduced/extracted from the chamber, to allow conductors 26 todeliver an excitation voltage to the electrodes, etc.

In addition to the chamber, FIG. 1 shows that the device 20 may alsoinclude a beam reverser 28 and outcoupler 30 cooperatively arranged toform an optical cavity. For the device 20, the beam reverser 28 may beas simple as a flat, fully reflective mirror or as complex as agrating-based line-narrowing unit. It is to be appreciated that the useof a moveable electrode is not limited to the stable, standing wavecavity alluded to above. Instead, a transverse discharge gas laserchamber having one or more moveable electrodes may be employed withinother optical arrangements such as a one-pass amplifier, multi-passamplifier, traveling wave amplifier such as a ring amplifier, unstablecavities, etc.

Continuing with FIG. 1, the device 20 may also include a pulse powersystem delivering electrical pulses to electrodes located within thechamber housing 22 a,b via conductors 26. Although the description thatfollows will be provided with reference to a pulsed laser device, it isto be appreciated that some or all of the concepts disclosed herein maybe equally applicable to continuous discharge gas laser devices whichhave electrodes that suffer a dimension change due to erosion or someother phenomenon. FIG. 1 further illustrates that during operation ofthe device 20, a laser beam 34 is created which exits the optical cavityvia the outcoupler 30.

FIG. 2 shows a multi-stage gas discharge laser device, generallydesignated 20′ to illustrate that the inter-electrode spacing may beindependently (or in some cases dependently) adjusted in one, both orall of the laser device chambers of a multi-stage device. For example,the first stage may be either a power oscillator, PO or a masteroscillator, MO. Typically, an oscillator is referred to as an MO if morethan about a third of the total laser output power is produced in theinitial oscillation cavity and is referred to as a PO if less than abouta third of the total output power is produced in the initial oscillationcavity. Subsequent stage(s) may be, for example, a one-pass poweramplifier, a multi-pass power amplifier, a power oscillator or atraveling wave amplifier such as a ring amplifier. It is to beappreciated that a multi-stage device may include some or all of thecomponents shown in FIG. 2, depending on the configuration. Thecomponents shown in FIG. 2 include a beam reverser 28′, first stagechamber 50, first stage outcoupler 30′, turning optics 52 a, b,incoupler 54, second stage chamber 56 and second stage outcoupler 58.

Inter-Electrode Spacing Adjustment

FIGS. 3A-D illustrate how electrode dimensional changes associated witherosion can affect the inter-electrode spacing and how the movement ofone electrode relative to the other may re-establish a more desirableinter-electrode spacing. In more detail, FIG. 3A shows the initialelectrode positions (prior to erosion) with electrode 60 spaced fromelectrode 62 to establish an initial inter-electrode spacing 64. FIG. 3Billustrates the electrodes 60, 62 after significant electrode erosionhas occurred resulting in inter-electrode spacing 66 (note initialinter-electrode spacing 64 is shown for reference purposes). FIG. 3Cillustrates the electrodes 60, 62 after significant electrode erosionhas occurred (FIG. 3B) and after electrode 62 has been moved in thedirection of arrow 68 resulting in an inter-electrode spacing that isclose to the initial inter-electrode spacing 64. FIG. 3D illustratesthat the electrode 62 may be moved to a position where its dischargesurface extends into the initial electrode gap (illustrated by thedotted lines) to accommodate erosion of electrode 60.

FIGS. 3A-D illustrate the case of asymmetric electrode erosion. Inparticular, it is clear from FIG. 3B that electrode 62 has eroded about10 times more than electrode 60. For this case, movement of electrode 62may be sufficient by itself (movement of electrode 60 may not berequired) to provide the desired inter-electrode spacing correction.This type of asymmetric electrode wear is common in certain types oftransverse discharge gas lasers such as some high-power, high repetitionrate, excimer lasers where the anode (the electrode electricallyconnected to the housing) typically erodes at a rate much greater thanthe cathode. Although FIGS. 3A-D illustrate asymmetric electrodeerosion, it is to be appreciated that one or both of the electrodes maybe moved to provide an inter-electrode spacing correction for a devicewhich experiences symmetric electrode wear. For systems where bothelectrodes are moveable, the electrodes may be moved to set a desiredinter-electrode spacing and/or may be used to move the discharge regionrelative to the other optics and apertures in the system. Thus, theelectrode movement system may be used as an alignment tool to adjust thebeam footprint relative to one or more system apertures/optics.

Inter-Electrode Spacing Control

For the device 20 shown in FIG. 1, the control of the inter-electrodespacing may be effectuated in several different ways. In perhaps thesimplest implementation, the inter-electrode spacing may be visuallyobserved, for example by looking through one of the windows 24 a, b, andthe observation used to move one or both of the electrodes. For example,a technician may use the observation to instruct a laser systemcontroller 70 via keypad or graphic user interface (or any othercontroller input device known in the art) to signal an actuator 72,which in turn, may drive a mechanism (see description below) to producethe desired inter-electrode spacing adjustment. For this purpose, alinkage 74 may pass through the wall of the chamber housing 22 a,b, anda flexible bellows 76 (or other suitable arrangement known in thepertinent art) may be provided to prevent laser gas from exiting thechamber housing 22 a,b. It is to be appreciated that portions (memory,processor, etc) or all of the controller 70 may be integral with (e.g.shared) or separate from a main laser system controller which controlsother laser functions such as discharge voltage, timing, shutteractivation, etc.

In another implementation, the inter-electrode spacing may be adjustedbased on a monitored device parameter. For example, the device 20 maymonitor one or more device parameters such as accumulated pulse count,average historical duty cycle, wavelength, gas pressure, runningvoltage, bandwidth, pulse-to-pulse energy stability (sometimes referredto as sigma), beam size, or a measured relationship between dischargevoltage and pulse energy. The device parameter(s) may be selected topredict the extent of electrode erosion (pulse count, average historicalduty cycle, etc.) and/or may be selected to tune the laser device toproduce an output beam having a desired characteristic (bandwidth,pulse-to-pulse energy stability, etc.).

As shown in FIG. 1, one or more of these device parameters may bemonitored by measuring a property of the output laser beam 34 using ameasuring instrument 78. A control signal indicative of the deviceparameter may then be output from the instrument 78 and transmitted tothe controller 70, which in turn, provides a signal to the actuator 72.Some device parameters, such as accumulated pulse count, averagehistorical duty cycle, etc, may be provided to the controller 70 orgenerated within the controller 70 without the use of a measuringinstrument. Thus, in at least some implementations envisioned herein, ameasuring instrument 78 may not be required. One the other hand, morethan one parameter (i.e., a plurality of device parameters) may becommunicated to, or developed within, the controller 70 for processingin an algorithm to determine an appropriate inter-electrode spacingadjustment.

In a particular implementation, a controller may be programmed to scanthe inter-electrode spacing over a pre-determined spacing range. Thus,the inter-electrode spacing may be adjusted either continuously orincrementally while the laser is operating and outputting laser pulses.During the scan, a measuring instrument or other laser component mayprovide one or more parameter inputs to the controller allowing thecontroller to determine a relationship between the parameter(s) and theinter-electrode spacing. From the relationship, the controller may thendeduce an optimum inter-electrode spacing and thereafter adjust theinter-electrode spacing accordingly.

Inter-Electrode Spacing Mechanisms

FIGS. 4A-E show the components of a first mechanism that may be coupledto an electrode 80 to produce an actuator-driven, electrode movement.For the mechanism, a first elongated rigid member 82 having sawtoothramp structure and a second elongated rigid member 84 havingcomplimentary sawtooth ramp structure are disposed within a channelformed in an electrode support bar 86, as shown in FIG. 4A (which showsthe electrode 80 in a fully retracted position) and 4B (which shows theelectrode 80 in a fully extended position). For the device, theelectrode support bar 86 is typically elongated, like the electrode andis affixed at its ends to the wall of the housing 22 a, b (see FIG. 1).

Perspective views of elongated rigid members 82 and 84 are shown inFIGS. 4C and 4D, respectively. As seen there, elongated rigid member 82is formed with a plurality of inclined, parallel surfaces, (of whichsurfaces 88 a-c have been labeled) and an opposed flat surface 90.Somewhat similarly, elongated rigid member 82 is formed with a pluralityof complementary, inclined, parallel surfaces, of which surfaces 92 a-chave been labeled) and an opposed flat surface 94 which includes araised flat portion 96 onto which the electrode 80 may be affixed (seeFIGS. 4A and 4E). Although FIG. 4C illustrates a rigid member 82 havingabout 20 inclined surfaces for a 30 cm electrode, it is to beappreciated that more than 20 and as few as one inclined surface may beused.

For the mechanism, as best seen in FIGS. 4E and 4F, the rigid members82, 84 are aligned longitudinally (i.e., each aligned parallel to thedirection of electrode elongation shown by arrow 98) and placed incontact with each other. Specifically, each inclined surface 88 a-c ofrigid member 82 is placed into sliding contact with a correspondinginclined surface 92 a-c of rigid member 84. As further shown in FIG. 4E,spring assemblies 100 a, b may be employed to maintain a preselectedcontact pressure between the inclined surfaces 88 a-c of rigid member 82and inclined surfaces 92 a-c of rigid member 84.

FIGS. 4E and 4F illustrate the movement of electrode 80 in response to amovement of the elongated member 82 relative to the electrode supportbar 86 with FIG. 4E showing the electrode 80 in a fully retractedposition and 4F showing the electrode 80 in an extended position.Comparing FIGS. 4E with 4F, it can be seen that a movement of elongatedrigid member 82 relative to the electrode support bar 86 in thedirection of arrow 102 will result in a movement of the electrode 80 andelongated rigid member 84 in the direction of arrow 104 Similarly,movement of elongated rigid member 82 relative to the electrode supportbar 86 in the direction opposite arrow 102 will result in a movement ofthe electrode 80 and elongated member 84 in the direction opposite arrow104 with the spring assemblies maintaining contact between the inclinedsurfaces 88 a-c, 92 a-c.

FIG. 4G shows a mechanism linkage which includes a substantiallystraight push rod 106 and an L-shaped pivoting lever 108 forestablishing a mechanical path between the actuator 72 and rigidsawtooth structure 82. With this arrangement, movement of the push rod106 in the direction of arrow 110 will cause the rigid sawtoothstructure 82 to move in the direction of arrow 102 (arrow 102 also shownin FIG. 4F). This in turn will cause a movement of the electrode 80 inthe direction of arrow 104 as shown in FIG. 4F. Note: the rigid member82 is disposed in a similarly sized channel formed in the support bar 86and as such is laterally constrained therein (see FIG. 4A).

FIG. 4G further shows that the actuator 72 may be affixed to the wall ofthe chamber housing 22 a and operable attached to a first end 112 of thepush rod 106. Push rod 106 then extends through an opening in the wallof the chamber housing 22 a to a second push rod end 114 which isdisposed inside the chamber. Flexible bellows 76 may be provided tomaintain gas pressure within the chamber while allowing translation ofthe push rod 106. Also shown, second push rod end 114 may be pivotallyattached, for example using a pin/cotter key arrangement (or anysimilarly functioning arrangement known in the art), to the L-shapedlever 108, which in turn is pivotally attached near its midsection tothe electrode support bar 86 at pivot point 116. End 118 of lever 108may be pivotally attached to rigid member 82, as shown. A simpler designmay be employed in which the push rod is aligned parallel to the rigidmember and attached directly thereto, however, use of the L-shaped lever108 allows for motion amplification/de-amplification depending on therelative lengths of the lever arms. If desired, the actuator may bereplaced by a drive screw (not shown) or similar component allowing formanual adjustment of the inter-electrode spacing. Another alternative tothe push rod/lever system is to use a pulley/cable system to move therigid member 82 within channel. For this alternative, the member 82 maybe biased away from the pulley using a spring attached to the supportbar.

Flexable Conductive Member

As best seen cross-referencing to FIGS. 4A and 5, a conductive, flexiblemember 120 may be provided for electrically shielding some or all of theinter-electrode spacing mechanism components and/or electricallyconnecting the electrode 80 to the current return tines 122 a-c and/orconstraining the electrode 80 and rigid member 84 from longitudinalmovement (i.e., movement in the direction of arrow 98 in FIG. 4E) and/orto provide a thermally conductive path allowing heat to flow from theelectrode to the support bar. In some applications, contacting surfacesof the electrode spacing mechanism may arc, and in extreme cases weldtogether, if unshielded in the presence of the electric fields generatedby discharge.

As shown in FIGS. 4A and 5, the flexible member 120 may have a firstflexible member edge 124 that is attached to electrode 80 and/or rigidmember 84 for movement therewith (note: for the embodiment shown, theedge 124 is clamped between electrode 80 and rigid member 84).Typically, the flexible member 120 is made of a conductive metal such ascopper or brass allowing the flexible member 120 to conduct heat and/orelectricity from the electrode 80 to the support bar 86/current returntines 122 a-c.

FIGS. 4A and 5 also show that the flexible member 120 may have a secondedge 126 that is attached to the support bar 86 and thus, may be heldfixed relative to the housing 22 a (see FIG. 1). FIG. 4A furtherillustrates that the edge 126 of the flexible member 120 may beelectrically connected to the current return tines 122 establishing anelectrical path from the electrode 80 to the tines 122. The currenttines, in turn, provide a relatively low impedance path from theflexible member 120 to a pulse power system 32 (shown in FIG. 1). Forthe device shown, the flexible member 120 may be formed with one or moreconvolutions 128 a-c, e.g. bends, that are aligned parallel to thedirection of electrode elongation (i.e. the direction of arrow 98 inFIG. 4E) to impart flexibility to the member. With this arrangement, theflexible member 120 may be described as having a planar, corrugatedshape.

As described above, the flexible member 120 may function to electricallyshield some or all of the inter-electrode spacing mechanism componentsand/or electrically connect the electrode 80 to the current return tines122 a-c and/or constrain the electrode 80 and rigid member 84 fromlongitudinal movement. Although a flexible member 120 may be designed toachieve all of these functions, it is to be appreciated that someapplications may not require all three functions. For example, for somedischarge power levels, shielding may not be required. Moreover, one ormore of the three functions may be performed by another component. Forexample, longitudinal constraint of the electrode 80 may be performed ina different manner allowing a flexible member 120 which lacks thestrength necessary to constrain the electrode 80. Other arrangements maybe provided which perform one or more of the functions described aboveincluding a member whose flexibility is derived from its thickness, aplurality of spaced apart flexible members and tines having one or moreconvolutions.

One feature of the structural arrangement shown in FIGS. 4A-G and 5 isthat the inter-electrode spacing can be adjusted without moving theelectrode support bar 86 relative to the other laser components, e.g.,fan, housing, etc.). This allows a close tolerance between the supportbar 86 and other structures to be maintained. For example, in someapplications, a close tolerance between the support bar 86 and a fan(not shown) may be maintained allowing the fan to run more efficiently.

Another feature of the structural arrangement shown in FIGS. 4A-G and 5is that a substantial heat transfer path is provided between theelectrode 80 and the support bar 86. In particular, the relatively largecontact area between the rigid member 82 and rigid member 84 and therelatively large contact area between the rigid members 82, 84 and thesupport bar cooperate to provide a substantial heat transfer path. Forsome applications, this path may be useful in preventing overheating ofthe electrode 80.

Another feature of the structural arrangement shown in FIGS. 4A-G and 5is that it maintains a relatively good parallelism between electrodesover the range of electrode movements.

FIGS. 6A and 6B show an alternative mechanism in which a camshaft 150may be rotated about a rotation axis 152 (which may be generallyparallel to the direction of electrode elongation) to provide electrodeextension with FIG. 6A showing the electrode 154 in a fully retractedposition and 6B showing the electrode 154 in an extended position. Forthe mechanism, the camshaft 150 may be in direct contact with theelectrode 154 (with or without a thermally conductive rigid memberestablishing a heat path from the electrode 154 to the support bar 158)or, as shown, a thermally conductive rigid member 156 may be interposedbetween the electrode 154 and camshaft 150 and used to conduct heat fromthe electrode 154 to the support bar 158. For the mechanism shown inFIG. 6, a flexible member 160 (as described above may be used toelectrically shield some or all of the inter-electrode spacing mechanismcomponents and/or electrical connect the electrode 154 to the currentreturn tines 162 and/or provide a heat conduction path from theelectrode 154 to the support bar 158. For the device, the camshaft 150may be rotated manually or by an energized actuator and may becontrolled by any of the techniques/structural arrangements describedabove.

FIG. 7A-7E show alternative mechanisms which include one or more drivescrews 170 to provide electrode extension with FIG. 7A showing theelectrode 172 in a fully retracted position and 7B showing the electrode172 in an extended position. For the mechanism, the drive screw(s) 170may be in direct contact with the electrode 172 (with or without athermally conductive rigid member establishing a heat path from theelectrode 172 to the support bar 174) or, as shown, a thermallyconductive rigid member 176 may be interposed between the electrode 172and drive screw(s) 170 and used to conduct heat from the electrode 172to the support bar 174.

For the mechanism shown in FIGS. 7A-7E, a flexible member 178 (asdescribed above may be used to electrically shield some or all of theinter-electrode spacing mechanism components and/or electrical connectthe electrode 172 to the current return tines 180 and/or provide a heatconduction path from the electrode 172 to the support bar 174.Cross-referencing FIGS. 7A and 7C, it may be seen that the drivescrew(s) 170 may extend through the wall 182 and be threaded through aprepared hole (i.e., drilled, reamed and tapped) in the support bar 174.Alternatively, a prepared hole may be provided in the wall 182 or someother structure or a nut (not shown) may be affixed to the wall 182 orsupport bar 174. A flexible bellows as described above (not shown) maybe employed at the wall 182 to prevent gas leakage from the chamber. Forthese mechanisms, each drive screw 170 may be rotated manually (fromoutside the chamber) or by an energized actuator 184 (shown with dashedlines to indicate an optional component) and may be controlled using oneor more of the techniques/structural arrangements described above.Springs 186 a,b may be provided to bias the electrode 172 relative tothe support bar 174 as shown in FIG. 7C.

FIG. 7D illustrates a mechanism having two drive screws 170 a,b that arespaced apart along the length of the electrode 172′ with each drivescrew 170 a, 170 b independently rotatable manually (from outside thechamber) or by energized actuators 184 a′, 184 b′, respectively (shownwith dashed lines to indicate an optional component).

FIG. 7E illustrates a mechanism having three drive screws 170 c,d,e thatare spaced apart along the length of the electrode 172″ with each drivescrew 170 c,d,e independently rotatable manually (from outside thechamber) or by energized actuators 184 c′, d′, e′, respectively (shownwith dashed lines to indicate an optional component).

For the mechanisms having two or more drive screw(s) 170 (FIGS. 7D and7E), each of the drive screws may be independently adjusted to adjustinter-electrode parallelism and/or inter-electrode spacing.Specifically, the drive screws may be independently adjusted until theelectrode 172″ is parallel to the other electrode in the discharge pair(dotted lines in FIG. 7D showing an unaligned electrode and solid linesshowing an electrode after alignment into parallel with anotherelectrode).

For mechanisms having three or more drive screw(s) 170 (FIG. 7E), eachof the drive screws 170 may be independently adjusted to adjustelectrode parallelism (as described above) and/or electrode curvatureand/or inter-electrode spacing. Specifically, the drive screws may beindependently adjusted until the electrode 172″ has a desired curvaturesuch as straight or having a curvature matching the other electrode(dotted lines in FIG. 7D showing a non-desired curvature and solid linesshowing an electrode after a curvature adjustment).

Movable Flow Guides

Although the electrode 80 shown in FIG. 4A has substantially straight,parallel sidewalls, it is to be appreciated that other electrode shapesmay be used in the devices described herein. For example, FIGS. 8A and8B show an electrode 200 having a tapered construction (in a planenormal to the direction of electrode elongation) in which the electrodewidth, ‘w’, decreases gradually from the electrode base 202 to theinitial discharge surface 204. Other electrode designs can include anhourglass shape (not shown) in which the electrode width decreases fromthe base to a minimum and increases thereafter to the initial dischargesurface.

FIGS. 8A and 8B also show that flow guides 206 a,b, which may be made ofan insulating ceramic material may be disposed surrounding the electrode200 on each side to control the flow of gas over the tip of theelectrode 200 and prevent the discharge from striking metal structuresadjacent to the electrode 200. For the case of electrodes havingparallel sidewalls (FIG. 4A) these guides may be affixed to the supportbar and may remain stationary with respect thereto. Comparing FIG. 4A to4B, it can be seen that extension of the electrode 80 with parallelsidewalls does not affect the spacing between the electrode sidewallsand stationary flow guides 206 a′, 206 b′. On the other hand, forelectrodes having non-parallel sidewalls, such as electrode 200 in FIG.8A, electrode extension may affect the spacing between the electrodesidewalls and stationary flow guides 206 a, b.

FIGS. 8A and 8B illustrate an arrangement in which the flow guides 206a, b are moveable attached to the support bar 208 allowing the flowguides 206 a, b to move apart (in the direction of arrows 210 a, b fromone another as the electrode 200 is extended (in the direction of arrow212). To effectuate this flow guide movement, each flow guide 206 a, bis form with a surface 214 that contacts the electrode 200 and isinclined at an angle relative to the direction of electrode movement(arrow 212) For the arrangement shown, one or more springs (not shown)may be provided to bias each flow guide 206 a, b toward the electrode200.

Electrode End Contour

FIG. 9 shows a pair of electrodes 218, 220 and illustrates an endcontour for a moveable electrode 220. As shown, electrode 218 is formedwith a relatively flat portion 222 where discharge is desired and beginsto curve away from the discharge region at point 224. Electrode 220 isshown with the solid line indicating its initial electrode shape and thedashed line indicating it end-of-life shape. As shown, the electrode 220is initially formed with a relatively flat portion 226 where dischargeis desired, a curved transition section 228 and a second flat section230. As shown, the flat section 230 may be spaced at a distance‘d.sub.1’ from the electrode base 232, the beginning-of-life flatsection 226 may be spaced at a distance ‘d.sub.2’ from the electrodebase 232, and the end-of-life flat section 234 may be spaced at adistance ‘d.sub.3’ from the electrode base 232, withd.sub.2>d.sub.1>d.sub.3. In a particular embodiment, the electrode 220is formed with d.sub.1=d.sub.3+n(d.sub.2−d.sub.3), where n is typicallyin the range of about 0.25 to 0.75, placing the flat section 230 betweenthe average height of the electrode 220 over the electrode's life. Forexample, d.sub.2−d.sub.3 may be about 3 mm One feature of thearrangement shown is that it confines the discharge to a selecteddischarge region (ending near point 224) over the life of the electrode220.

While the particular embodiment(s) described and illustrated in thispatent application in the detail required to satisfy 35 U.S.C. sctn.112are fully capable of attaining one or more of the above-describedpurposes for, problems to be solved by, or any other reasons for orobjects of the embodiment(s) above described, it is to be understood bythose skilled in the art that the above-described embodiment(s) aremerely exemplary, illustrative and representative of the subject matterwhich is broadly contemplated by the present application. Reference toan element in the following Claims in the singular is not intended tomean nor shall it mean in interpreting such Claim element “one and onlyone” unless explicitly so stated, but rather “one or more”. Allstructural and functional equivalents to any of the elements of theabove-described embodiment(s) that are known or later come to be knownto those of ordinary skill in the art are expressly incorporated hereinby reference and are intended to be encompassed by the present Claims.Any term used in the Specification and/or in the Claims and expresslygiven a meaning in the Specification and/or Claims in the presentApplication shall have that meaning, regardless of any dictionary orother commonly used meaning for such a term. It is not intended ornecessary for a device or method discussed in the Specification as anembodiment to address or solve each and every problem discussed in thisApplication, for it to be encompassed by the present Claims. No element,component, or method step in the present disclosure is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the Claims. No claim element in theappended Claims is to be construed under the provisions of 35 U.S.C.sctn.112, sixth paragraph, unless the element is expressly recited usingthe phrase “means for” or, in the case of a method claim, the element isrecited as a “step” instead of an “act”.

What is claimed is:
 1. A movable electrode assembly for use in a lasersystem, comprising: a first electrode having a first discharge surface;a second electrode having a second discharge surface, the secondelectrode being arranged opposite from the first electrode, the seconddischarge surface being spaced apart from the first discharge surface byan inter-electrode spacing having an initial spacing; an inter-electrodespacing mechanism interfaced with at least one of the second electrodeor the first electrode, the inter-electrode spacing mechanism configuredto adjust the inter-electrode spacing to the initial spacing; and anelectrical shield disposed between the inter-electrode spacing mechanismand at least one of the second electrode and the first electrode, theinter-electrode spacing mechanism including: a camshaft in contact witha first surface of the at least one of the second electrode or the firstelectrode, the camshaft including at least one cam and an axis ofrotation, the first surface being disposed opposite from thecorresponding first discharge surface or second discharge surface of theleast one of the second electrode or the first electrode; and anactuator coupled to the camshaft, the actuator configured to rotate thecamshaft around the axis of rotation.
 2. The system of claim 1, whereinthe inter-electrode spacing mechanism further includes a tensionmechanism to maintain a preselected contact pressure between thecamshaft and the least one of the second electrode or the firstelectrode.
 3. The system of claim 1, wherein the actuator is selectedfrom the group of actuators consisting of a piezoelectric actuator, anelectrostrictive actuator, a magnetostrictive actuator, a stepper motor,a servo motor, a voice coil actuator, a linear motor and a combinationthereof.
 4. The system of claim 1, further comprising a controllercoupled to the actuator and capable of generating a control signal, andwherein the actuator is responsive to the control signal to adjust thedischarge gap including moving the second electrode relative to thefirst electrode.
 5. The system of claim 1, wherein the at least one camincludes a plurality of cams.
 6. The system of claim 1, wherein firstelectrode, the second electrode and the inter-electrode spacingmechanism are included within a discharge chamber and wherein theactuator is external from the discharge chamber.
 7. The system of claim6, further comprising an electrode support bar attached to the dischargechamber, the second electrode moveable relative to the support bar, theinter-electrode spacing mechanism providing a heat conduction path fromthe second electrode to the support bar.
 8. The system of claim 6,wherein the actuator is coupled to the inter-electrode spacing mechanismby a linkage and wherein the linkage passes through an opening in a wallof the discharge chamber.
 9. The system of claim 1, further comprising aconductive member coupled to the second electrode and a support barcoupled to and supporting the second electrode.
 10. The system of claim9, wherein the conductive member includes one or more convolutions. 11.The system of claim 9, wherein the conductive member is flexible. 12.The system of claim 9, wherein the conductive member forms a shieldprotecting the inter-electrode spacing mechanism from electromagneticfields generated in the inter-electrode spacing.
 13. The system of claim1, wherein the first electrode and the second electrode are elongatedelectrodes wherein the first electrode and the second electrode arealigned longitudinally.
 14. The system of claim 1, further comprising acontroller, the controller configured to scan the spaced apart settingof the first electrode and the second electrode and trigger theinter-electrode spacing mechanism to move either of the first electrodeor the second electrode, or both, to position the discharge surfaces ofthe first electrode and the second electrode toward a desiredinter-electrode spacing.
 15. A movable electrode assembly for use in alaser system, comprising: a first electrode having a first dischargesurface; a second electrode having a second discharge surface, thesecond electrode being arranged opposite from the first electrode, thesecond discharge surface being spaced apart from the first dischargesurface by an inter-electrode spacing having an initial spacing; aninter-electrode spacing mechanism interfaced with the first electrode;and an electrical shield disposed between the inter-electrode spacingmechanism and the first electrode, the inter-electrode spacing mechanismincluding: a camshaft in contact with a first surface of the firstelectrode, the camshaft, the first surface being disposed opposite fromthe first discharge surface; and an actuator coupled to the camshaft,the actuator configured to adjust the inter-electrode spacing to aselected spacing.
 16. A movable electrode assembly for use in a lasersystem, comprising: a first electrode having a first elongated dischargesurface; a second electrode having a second elongated discharge surface,the second elongated discharge surface being arranged opposite from andparallel to the first elongated discharge surface, the second elongateddischarge surface being spaced apart from the first elongated dischargesurface by an inter-electrode spacing having an initial spacing; aninter-electrode spacing mechanism interfaced with the first electrode;and an electrical shield disposed between the inter-electrode spacingmechanism and the first electrode, the inter-electrode spacing mechanismincluding: a camshaft in contact with a first surface of the firstelectrode, the camshaft, the first surface being disposed opposite fromthe first elongated discharge surface; and an actuator coupled to thecamshaft, the actuator configured to adjust the inter-electrode spacingto a selected spacing.